That's an enormously broad question.
Have you priced an LS and trans? Which LS? A good drivetrain will cost more than your G is worth... you'll also need an 07+ engine to maintain any semblance of legality, unless you live in a non-emissions state.
Further, if you're incapable of changing a head gasket, the fabrication and electronics of a complete drivetrain swap is probably out of your reach (for now).